1. Field of the Disclosure
The present disclosure relates generally to the field of exploration and production of hydrocarbons from wellbores. More specifically, the present disclosure relates to an apparatus used for storing connate fluid sampled from within a subterranean geological formation.
2. Description of Related Art
The sampling of fluids contained in subsurface earth formations provides a method of testing formation zones of possible interest by recovering a sample of any formation fluids present for later analysis in a laboratory environment while causing a minimum of damage to the tested formations. The formation sample is essentially a point test of the possible productivity of subsurface earth formations. Additionally, a continuous record of the control and sequence of events during the test is made at the surface. From this record, valuable formation pressure and permeability data as well as data determinative of fluid compressibility, density and relative viscosity can be obtained for formation reservoir analysis.
Early formation fluid sampling instruments were not fully successful in commercial service because they were limited to a single test on each trip into the borehole. Later instruments were suitable for multiple testing; however, the success of these testers depended to some extent on the characteristics of the particular formations to be tested. For example, where earth formations were unconsolidated, a different sampling apparatus was required than in the case of consolidated formations.
Downhole multi-tester instruments have been developed with extensible sampling probes for engaging the borehole wall at the formation of interest for withdrawing fluid samples therefrom and measuring pressure. In downhole instruments of this nature it is typical to provide an internal draw-down piston which is reciprocated hydraulically or electrically to increase the internal volume of a fluid receiving chamber within the instrument after engaging the borehole wall. This action reduces the pressure at the instrument/formation interface causing fluid to flow from the formation into the fluid receiving chamber of the tool or sample tank. Heretofore, the pistons have accomplished suction activity only while moving in one direction. On the return stroke the piston simply discharges the formation fluid sample through the same opening through which it was drawn and thus provides no pumping activity. Additionally, such unidirectional piston pumping systems can only move the fluid being pumped in a single direction, resulting in a slowly operating sampling system.
As shown in FIG. 1, the sampling of subterranean formation fluid typically involves the insertion of a sampling tool 10 within a wellbore 5 that intersects the subterranean formation 6. Generally the tool 10 is inserted on the end of a wireline 8 or other armored cable, but can also be disposed within the wellbore 5 on tubing (not shown). When wireline 8 is used, it is typically maintained on a spool from which the tool 10 is reeled within the wellbore 5. When it is established that the tool 10 is adjacent to the region of the formation 6 where sampling is to occur, rotation of the spool is ceased thereby suspending the tool 10 at the proper depth within the wellbore 5. Upon suspending the tool 10 at the predetermined downhole depth, an urging means 12 is extended from the tool 10 that pushes the tool 10 against the inner diameter of the wellbore 5 on the side of the tool 10 opposite to the urging means 12. A probe 14 provided on the tool 10 opposite to the urging means 12 pierces the wellbore 5 inner diameter or wall extending a small distance into the formation 6. The probe 14 includes a passage within its body allowing for fluid flow through its inner annulus. Within this annulus of the probe 14, subterranean fluid can flow from the formation 6 to within the tool 10 for storage and subsequent analysis.